Lm35dz

[PeterDove]

Hi All,

I have an idea about charging batteries using the main/solar.

Lets say that I have a current source of 300ma. I want to use an LM35DZ which if I read correctly has a range of 0 deg. C to 100 deg C. Each degree amounts to another 10mV added to the output. What I want is some way to limit the current based on the temperature of the batteries. Now I have learned that NPNs can be used to control the amount of Current based on the current applied to the base. However the current coming from the middle leg of the LM35DZ is pretty damn small.

Does anyone have an idea of what I can drive from the temperature voltage of the LM35DZ which can control the size of the 300mA current?

PS. I really want to keep things to simple readily available components - so monolithic IC etc are out of the question. If it can be kept down to simple components like transistors, capacitors, resistors etc that would be super.

Thanks

Peter Dove

 

[Nigel Goodwin]

An LM35 is an IC, so what's wrong with using a simple opamp?. You certainly don't need anything as complicated as that - a simple thermistor feeding an opamp/comparator could turn the charging current off if the batteries get too hot.

 

[PeterDove]

An LM35 is an IC, so what's wrong with using a simple opamp?. You certainly don't need anything as complicated as that - a simple thermistor feeding an opamp/comparator could turn the charging current off if the batteries get too hot.

Cause I have an LM35 I'll look at an opamp.. (whatever that is )

Cheers

Peter

 

[Nigel Goodwin]

If you don't even know what an opamp is, I can see you're going to have problems!. Check out and look at the circuit 'Auto-Fan' for what you want to do.

 

[PeterDove]

If you don't even know what an opamp is, I can see you're going to have problems!. Check out and look at the circuit 'Auto-Fan' for what you want to do.

Thanks - read it, looked up op-amp made a simulation in my software - got the result I wanted using an op amp, transistor and my LM35 - thanks a lot

no problem some people can learn pretty quick

Thanks

Peter

 

[audioguru]

Be careful, Peter.
If your rechargable battery is Ni-Cad or Ni-MH, when it gets too hot its vent opens to release the pressure. It might leak after.

If your rechargable battery is Lithium, when it gets too hot it gets hotter and hotter even with the current turned off and it catches on fire with a hot white flame like magnesium.
You don't want that so manufacturers recommend backup systems to prevent over-charging if one system fails.

 

[PeterDove]

Be careful, Peter.
If your rechargable battery is Ni-Cad or Ni-MH, when it gets too hot its vent opens to release the pressure. It might leak after.

If your rechargable battery is Lithium, when it gets too hot it gets hotter and hotter even with the current turned off and it catches on fire with a hot white flame like magnesium.
You don't want that so manufacturers recommend backup systems to prevent over-charging if one system fails.

Thanks, I am using NIMH. I am kinda hoping that the LM35 doesnt fail! LOL - Anyway I will post up the circuit for inspection later when I have it presentable and I am fully satisfied I have done my best with it.

Peter

 

[audioguru]

The shorter is the charging time then the higher is the charging current and the higher is the risk of overcharging.

For 1 hour charging of Ni-MH, Energizer recommends charging to 90% of full charge with a voltage detect IC or a temperature probe. One of them is the backup.
Then they say to top up the charge at 1/10th of the original current and detect full charge with the voltage detect IC or temperature probe. Then they say to reduce a trickle charge current to 1/40th of the battery's rating.
Read their Ni-MH Applications Manual at www.energizer.com and click on Technical Info at the top.